1. Field of the Invention
The invention relates to transmissions. In particular, the invention relates to split-axis hybrid transmissions for vehicles.
2. Related Art
Transmissions provide varying torque ratios between power sources, such as engines or motors, and the drive axles to provide efficiency and higher performance in vehicles. Previously known transmissions inherently include many sources of power loss and inefficiency. Manual transmissions lose power during gear ratio changes while the engine or motor is disengaged when the transmission elements are shifted to the next desired gear ratio. Automated mechanical transmissions improved on manual transmission by automatically determining when a gear shift would be advantageous. However, most automated mechanical transmissions, like manual transmissions, lose power during shifting when the transmission must first shift into neutral before changing the gear ratio.
The powershift automatic transmission is an improvement over traditional automatic mechanical transmissions in that it does not require decoupling the power source during a gear ratio change. Nonetheless, powershift automatic transmissions still suffer from power losses associated with released multi-plate clutches and pumping losses for lubrication and clutch actuation flow.
The dual-clutch transmission reduces the overall ratio changing time relative to an automated manual transmission, since an overlap can be performed during the shift, which results in less disturbance of torque during a shift. When the transmission shifts to the next gear ratio, one clutch disengages the transmission from the current gear while the other clutch engages the transmission in the target gear. Thus, power flows almost constantly from the drive mechanism to the wheels of the vehicle. Dual-clutch transmissions have the advantages of using a smaller oil pump and eliminating the multi-plate clutches used in a powershift automatic transmission. These two differences provide reductions in parasitic losses. However, dual-clutch transmissions are only able to preselect one gear ratio at a time. If the transmission incorrectly predicts the next gear ratio, then excessive delays in the shift event may occur, and the transmission may be forced to remain in neutral or the incorrect gear ratio for an extended period of time. This results in reduced performance and driveability.
Thus, there is a need for a highly efficient, cost-effective transmission with improved capabilities for preselecting a target gear and for minimizing torque interruption during a gear change.